Surgical sutures and attached surgical sutures are well known in the art. During the course of a surgical procedure, it is typically necessary for the surgeon to use surgical needles and attached sutures for a variety of purposes, including to approximate tissue. It is desirable, in many of these procedures, that the maximum diameter of the needle, typically the diameter at the blunt or proximal end of the needle, and the maximum diameter of the suture be as close to the same size as possible, and it is also advantageous for the suture diameter to be larger. This design is necessary or desirable so that a hole and pathway in tissue resulting from a surgeon passing the needle through the tissue during a surgical procedure is substantially filled by the body of the suture. This is especially important when joining or approximating highly vascularized tissue in order to prevent oozing or seepage of blood through the pathway and hole produced by the needle. In addition, pathways for bacteria are effectively closed off to prevent infections. Originally, most surgical needles had an eye at their blunt or proximal ends through or in which a surgical suture was mounted or attached. As can be appreciated, this meant that the blunt end of the needle had to have a sufficient size to allow for an eye to be placed in the blunt end of the needle and to accommodate at least double the maximum diameter of a suture strand folded around the eye feature of the needle. This doubling of the suture and the requisite increased size of the blunt end of the needle resulted in a needle-suture combination with a large cross-sectional area that was passed through the tissue. The resulting hole and pathway in the tissue, produced when the needle was passed through tissue, was substantially greater than the cross-sectional area of the attached suture remaining within the tract to approximate or fix the tissue; as described herein, such a pathway may lead to post-implantation complications such as bleeding, infections, etc.
Over the years, in order to improve surgical procedures and patient outcomes, various techniques have been developed to eliminate the eye in the blunt or proximal end of the needle and find other techniques or methods by which a suture strand can be attached to the blunt or proximal end of a surgical needle. One example of an improved suture attachment technique that has been developed is the forming of a channel in the blunt or proximal end of a needle by a conventional metal forming process. In order to attach an end of a suture to a surgical needle having a channel, the distal end of the suture is placed in the channel and the channel is mechanically swaged in a conventional manner to mechanically secure the suture end in the needle channel. Another technique known in this art for attaching suture strands to surgical needles is to drill a bore hole into the proximal end of a surgical needle using conventional processes such as laser drilling and mechanical drilling. In a similar manner, the distal end of a surgical suture is placed into the bore hole and the proximal end of the needle containing the bore hole is conventionally mechanically swaged, although other attachment or securement methods may be used such as gluing. As can be appreciated, it is still required that the diameter or maximum dimension of the blunt or proximal end of a needle having a suture mounting channel or bore hole be substantially larger than the diameter of the body of an attached suture, and hence when such needle-suture combinations are used to join tissue, the suture still does not completely fill the resulting hole and pathway in tissue formed by the needle.
Processes have evolved that may produce a multi-diameter suture, wherein the body of the suture is substantially larger than the portion of the suture (i.e., the tip) that is attached or mounted to a non-eyed needle, either in a channel or bore hole. The processes known in the art for producing reduced diameter suture tips typically alter the flexibility of the suture in the reduced sections in a negative manner by causing an increase in fiber stiffness or a loss of suture diameter consistency, thereby producing variable needle attachment strength. There remains a need in this art for novel processes and apparatuses to produce a suture with a novel tip section having a reduced cross sectional area that maintains the suture material properties of yield stress and suture flexibility at the needle attachment location, while providing consistent needle attachment strength through improved suture tip physical dimensions. There have been various approaches to suture tipping in the art.
U.S. Pat. No. 3,890,975 (McGregor), discloses a braided suture that is subjected to sizing through the application of tension when dipped in a liquid resin solution. The suture is dried to remove the solvent and to allow the coated region to solidify. Since the braided suture is subjected to tension, there is a reduction in diameter as the braided elements begin to align axially thereby compacting the core fibers. As the liquid resin dries, the coated region or tip of suture containing the tensioned coated fibers is locked into the reduced diameter configuration. The uncoated region resumes the original diameter when the tension is released. The sizing operation is conducted to ensure that the suture will release at a more consistent force from the needle after crimping. This process is only applicable to braided sutures, and the final suture diameter is dependent upon the quality or density of the braided suture utilized.
U.S. Pat. No. 4,832,025 (Coates), discloses a method for treating braided sutures that involves melt fusion of the tip region for insertion into a surgical needle. The suture is heated to an elevated temperature sufficient to effectively “melt fuse” a portion of the outer filaments of the multifilament suture. Such temperatures are typically in the range of about 260° C. to 300° C. (500° F. to 572° F.). The suture then stiffens upon cooling. Surface melting of the outer filaments has the effect of holding the filaments together when the suture is cut. It also causes stiffening of the suture which facilitates insertion of the suture end into the drilled bore hole of a needle. However, this melt fusion process has several significant drawbacks. Firstly, the melt fusion of filaments weakens the suture, whose tensile strength is degraded in proportion to the extent of melt fusion. Secondly, melt fusion causes an irreversible change in the suture filaments, which results in permanent stiffening and significant loss of the outer braided sheath tensile strength; and, this may result in sheaths that fracture and release independent of the core fibers causing bunching of the suture sheath during use.
U.S. Pat. No. 5,007,922 (Chen, et al.) discloses a method of producing monofilament sutures with regions of reduced diameter suture. The suture is wound in a helical or spiral configuration about a drum unit. The drum unit contains a region that is capable of expanding to produce an effectively larger perimeter dimension about the drum through the use of a split drum design. Once the fiber is wound about the perimeter of the drum, a heating element is positioned against the side of the drum tangentially along an axis that is parallel to the central axis of the drum. The heating element increases the temperature of any suture that is exposed along this line of contact along the side of the drum. After a satisfactory amount of heating has occurred, the drum is actuated such that the perimeter of the drum is increased. Since the suture is wound about the perimeter of the drum, the regions of heated suture are drawn down to accommodate the change in this dimension. This process results in reduced diameter regions within the suture that are highly oriented, beyond the orientation of the remaining non-heated regions of the suture. In addition to the change in molecular alignment, the resultant suture diameters of the exposed regions will vary depending upon the amount of deformation experienced in either overheated or under-heated segments of fiber windings.
U.S. Pat. No. 8,216,497 (Lindh, et al.) discloses various methods for forming tissue holding devices having predetermined shapes suitable for use in surgical applications, and devices formed in accordance with such methods are also provided. These methods include press-forming methods, and press-forming methods in combination with profile punching. Tissue holding devices formed in accordance with such methods include various configurations for a core and a plurality of tissue holding elements, such as barbs, extending outwardly from the core. The processes provide a method to shape an extruded fiber, at an elevated temperature, into a broader configuration that enables punch press-type technology to be applied to remove sections of the formed fiber component to form solid barbed elements. Their intention is to maintain a center region that is closer to the cross-sectional area of a traditional suture with appendages essentially extending from this core. Since the cross-sectional area of the core of the fiber is sized to be equivalent to a comparative non-barbed suture, the strength is essentially the same as the traditional comparative fiber. The process, as disclosed, relies on the displacement of the entire length of fiber to produce a uniform billet that is to be subjected to punching of the fiber. The punching operation produces a fiber with an oval configuration with extensions from a central core region to ensure that the fiber meets the knot tensile strength requirements for a comparably sized round suture. Due to the large displacement of the entire fiber volume to create a pre-punch billet, the straight tensile strength of the suture body is reduced relative to an unformed extruded suture because of the loss of orientation in the bulk forming process. Additionally, due to the reliance of bulk billet production, the process of forming and cutting cannot be linked into a continuous form and cut process due to the space required for said production.
Although the suture tipping processes of the prior art are adequate for their intended purpose, there are certain deficiencies attendant with their use. The deficiencies include loss of flexibility of the suture in the tipped region, fibrillation of the tipped region, alteration of the suture material yield stress, variability in finished tip geometry and limited applicability to non-braided sutures.
There is a need in this art for novel suture tipping processes and novel apparatuses for producing monofilament sutures having novel tip structures or sections that overcome the disadvantages of the processes of the prior art.